I've never had a leak in an air mattress. For the PCT, I used Montbell's torso pad plus "toggles to it" pillow system, but I put that on TOP of a full length 3/8" pad.
My reasoning was that for the first 700 miles I wanted the thick 3/8" ccf pad in part to prevent things from degrading or popping my ccf pad, in part to add more cushioning, and in part so I could use the pad as thermal protection *against* heat for a siesta during the day. I never actually did the latter as in my year we were fairly fortunate with the heat (at least I was), but it was there as an option. The full length ccf pad was also kind of deluxe for taking a lunch break during the day.
I kept the 3/8" pad in the Sierras on the theory that I wanted the thermal protection at night. And by the time I was through the Sierras I was strong enough and sleeping comfortably enough with that system that I just stuck with it.
I think that if I were doing it again (tempting ...), I'd go with a torso-length Neo-air and a 1/4" ccf thinlight pad for the first thousand miles (plus maybe a sitpad), then swap to a 1/8" thinlight thereafter. Or maybe just a 1/8" thinlight throughout. Neo-air plus thinlight(s) got me through the AT this year fine with --- again --- nary a leak.